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Pass return value of a function in background process

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Top Forums Shell Programming and Scripting Pass return value of a function in background process
# 8  
Old 02-15-2016
If you need really put something to do in background, then do something (parallel) and after that wait the child process to end, solution could be something like:

Code:
child()
{
  parentfile=$1

  do_something
  stat=$?

  echo "mypid=$$
           mystat=$stat" > $parentfile
}


#########
# MAIN

# file to use get answer from child process
childfile=$$.child.txt

# start child
child $childfile >/dev/null 2>&1  &
# save child process PID
CHILDPID=$!

do_something

# wait child process to end
wait $CHILDPID

# source childfile answer
. $childfile
# and destroy it
rm -f $childfile 2>/dev/null 

# use values
echo "child pid=$mypid"
echo "stat=$mystat"

Other method is to use event methods to communicate between process (trap + kill). Use file to move values between process. I like more event methods. There are not any shared variables. Of course you can use also named pipes between process. Source file is so easy.
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LEARN ABOUT X11R4

shell

shell(1F)							   FMLI Commands							 shell(1F)

NAME

       shell - run a command using shell

SYNOPSIS

       shell command [command] ...

DESCRIPTION

       The  shell  function  concatenate  its arguments, separating each by a space, and passes this string to the shell ($SHELL if set, otherwise
       /usr/bin/sh).

EXAMPLES

       Example 1: A sample output of shell command.

       Since the Form and Menu Language does not directly support background processing, the shell function can be used instead.

       `shell "build prog > /dev/null &"`

       If you want the user to continue to be able to interact with the application while the background job is running, the  output  of  an  exe-
       cutable	run  by shell in the background must be redirected: to a file if you want to save the output, or to /dev/null if you don't want to
       save it (or if there is no output), otherwise your application may appear to be hung until the background job finishes processing.

       shell can also be used to execute a command that has the same name as an FMLI built-in function.

NOTES

       The arguments to shell will be concatenate using spaces, which may or may not do what is expected. The variables set in local  environments
       will not be expanded by the shell because "local" means "local to the current process."

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       sh(1), attributes(5)

SunOS 5.10							    5 Jul 1990								 shell(1F)